Monoflanges combine the function as high as three valves in an especially compact body, because of a precise network of internal passages and valve chambers. But what really happens inside a monoflange valve, once installed?
In a chemical process a higher response speed is required for some control applications. Among the variables that affect the response time is the volume and the length between process and instruments. If the medium to be measured is gas, and the procedure tends to fluctuate strongly at times or if the control is critical, mounting the instrument near the process may be the solution.
Vibrations are also critical, for example, if impulse lines are connected to a vessel. The longer the hook-up, the wider is the amplitude of the vibration causing possible failures of the nozzle. A monoflange includes one, two or three needle valves inside a compact, flange-shaped body, allowing a substantial reduction in volume, dimensions, weight and potential leakage points.
Monoflange may be the solution
With respect to the requirements of the plant it is installed in, the monoflange can incorporate one, several valves. In a monoflange with two valves (block & bleed), one valve (with a blue cap) isolates the procedure and another (with a red cap) regulates the venting of the medium trapped inside the instrument. This is mostly found in applications which are relatively uncritical (e.g. low pressure) or in which a first shut-off valve is provided right before the monoflange.
The safest configuration, and the one we advise for aggressive media or critical operating conditions, may be the three-valve monoflange or the so-called double block & bleed (DBB), which features two shut-off valves in series and one valve for venting.
Monoflange functionality
The monoflange bodies are drilled internally with holes which connect the annular valve chambers.
The following picture illustrates the procedure inside a DBB monoflange:
The flow enters the monoflange from the pipeline and stops below the first shut-off valve [1];
When the first shut-off valve [1] opens, the flow proceeds towards the next shut-off valve [2] ; when the valve [2] is open, the instrument is thus linked to the process line;
When the first shut-off valve [1] is closed, the medium trapped between valve and instrument could be discharged via the vent valve [3] through the vent outlet. Both shut-off valves [1, 2] come in an angled position, that allows the flow to pass through them.
The two shut-off valves allow an improved isolation from the procedure: In case the first shut-off valve will not isolate the medium properly, the second one will become a safety means against accidental leaks. In some instances, customer specifications don’t allow the medium to be in touch with the instrument when it’s not measuring. That is why the medium shall be discharged utilizing the vent line. In other cases ? as a result of vent line ? instruments could be easily calibrated without dismounting them from the line.
Note
More info on our valves can be found on the WIKA website or in the video What is a monoflange? Assuming เกจวัดแรงดันไอน้ำ have any questions, your contact will gladly assist you to.